1. Field of the Invention
The present invention relates to a surface emitting laser device including an optical sensor and optical waveguide device employing the same, and more specifically, to a surface emitting laser device in which a surface emitting laser and an optical sensor are simultaneously integrated and the optical sensor is capable of responding within a wide wavelength band without affecting the optical output performance of the surface emitting laser, and optical waveguide device employing the same.
2. Discussion of Related Art
Recently, a surface emitting laser applicable in the field of optical communications has been the focus of considerable attention due to its ease of high-density integration, low power consumption, and low cost. In addition, since there is often need to transmit a signal from one point to another point at a remote site, and also receive back a signal from the point at the remote site through the same line, there is increasing need for a module having a light source and an optical sensor integrated therein.
In particular, there have been various suggestions for integrating a surface emitting laser with an optical sensor using structural characteristics of the surface emitting laser.
Generally, forms in which a surface emitting laser is integrated with an optical sensor include an integrated structure having a PIN photodetector disposed above a surface emitting laser along an optical output path thereof, an integrated structure having an absorbent layer disposed inside a resonator of a surface emitting laser, a structure having an absorbent layer disposed on a surface emitting laser and an optical sensor disposed adjacent thereto, a structure having a metal-semiconductor-metal (MSM) photodetector disposed on a surface emitting laser and at a location adjacent thereto, a structure having a surface emitting laser and an optical sensor disposed adjacent to each other, and so on. Such integrated structures have applications in optical coupling and two-way communication of surface emitting lasers and for monitoring and controlling optical output power of a surface emitting laser.
These methods for integrating a surface emitting laser with an optical sensor have the characteristics as described below.
First, the integrated structure having a PIN photodetector disposed above the surface emitting laser along the optical output path has the benefit of directly sensing output light by absorbing a part of the output light.
However, this structure has the drawback of a loss in output light and affects on the operation of the laser caused by the reflectance change of output light.
The integrated structure having an absorbent layer disposed inside a resonator of a surface emitting laser shows very good characteristics. However, its characteristics are sensitive to an absorption band of the absorbent layer and change in the location of the absorbent layer within the resonator. And in particular, it has a weakness with regard to environmental changes such as a temperature change.
The structure having absorbent layers disposed on a surface emitting laser and an optical sensor disposed adjacent thereto, and the structure having a metal-semiconductor-metal (MSM) photodetector disposed on a surface emitting laser and at a location adjacent thereto have a disadvantage in that an optical sensor or MSM photodetector grown on a thickly grown structure is hardly suitable for high-speed and high-sensitivity operation.
The structure having a surface emitting laser and an optical sensor disposed adjacent to each other has the advantage of a large optical sensor response. However, due to a narrow response bandwidth, it cannot be used for applications like two-way communication using considerably different wavelength bands for transmitting signals in either direction.
Accordingly, there is need for an integrated surface emitting laser and optical sensor, and method for their integration, that overcome the drawbacks of the conventional technology so that the performance of the surface emitting laser is unaffected by the optical sensor and the optical sensor independently exhibits high performance and can respond within a wide wavelength band.